Certain organisms including plants and some microalgae use a type II fatty acid biosynthetic pathway, characterized by the use of discrete enzymes in a multimeric complex for fatty acid synthesis. In contrast, mammals and fungi use a single, large, multifunctional protein.
In organisms that use a type II fatty acid biosynthetic pathway, β-ketoacyl-ACP synthase I (KAS I, EC 2.3.1.41) is one of the enzymes responsible for elongation of growing medium-chain fatty acyl-ACP from 4 to 16 carbon atoms in length. KAS I uses C2-C14 acyl-ACPs as substrates for condensation with a C2 unit derived from malonyl-ACP. KASIV is a related enzyme that serves a similar elongation function. Thus, KASI and KASIV can both be considered KASI-like enzymes.
Such genes have been introduced to plants using recombinant DNA technology. See for example U.S. Pat. No. 7,301,070, U.S. Pat. No. 6,348,642, U.S. Pat. No. 6,660,849, U.S. Pat. No. 6,770,465 and US2006/0094088 (of which ¶¶ 194-200 and the entirety of the document are hereby incorporated herein by reference). In plastidic cells such as those from plants, macroalgae and microalgae, KAS I-like enzymes are located in the chloroplasts or other plastids together with other enzyme of the fatty acid synthesis (FAS) pathway.
PCT publications WO2010/063032, WO2011/150411, WO2012/106560, and WO2013/158938 disclose genetic engineering of oleaginous microalgae including targeting of exogenous FAS gene products to the microalgal plastid.